1. Field of the Invention
This invention relates to information security.
2. Description of the Related Art
A technique has been known heretofore as a technique to improve the security of a digital signature in which the record of a signature is kept as a history when it is issued, the history data is reflected on a signature when the signature is to be issued newly to thereby build a logical chain relation between these signatures (referred to as hysteresis signature depending on the case).
The above-mentioned hysteresis signature technique is disclosed in Japanese Published Unexamined Patent Application No. 2001-331104.
A technique to provide a service for preventing denial of document preparation and transmission by a reliable third party organization is disclosed in, for example, ISO (the International Organization for Standardization) and IEC (the International Electrotechnical Commission), “INTERNATIONAL STANDARD ISO/IEC 13888-2 Information technology—Security techniques—Non-repudiation—Part 2: Mechanisms using symmetric techniques”, first edition, (Switzerland), 1998.4.1.
The above-mentioned hysteresis signature technique involves a method in which the signature history relating to the signature is used when the signature is verified. Therefore, a hysteresis signature verification method that reflects reliability of the signature history adequately has been desired.
It is a heavy burden for general signatures and signer side apparatus to store signature histories issued by means of the above-mentioned hysteresis signature for long time. Therefore, a storing method for mitigating the burden for storing signature histories of general users has been desired.
The ISO/IEC document discloses denial prevention service in which a token for guaranteeing the existence of the data to be guaranteed that has been sent to a reliable third party organization is issued and sent back, but does not discloses the data storage. Furthermore, the above-mentioned service is insufficient in checking of the signature history of verification target data as the service to guarantee the validity of the hysteresis signature.